[GAP Forum] list simple groups, again

[Hulpke,Alexander]

Dear Forum, Dear Keith,

> Is there something wrong with my installation?
No. Both issues are in the released code.

You encounter two different issues where particular cases have not yet been implemented. As they occur only for comparatively large groups I felt the functionality for simple groups was valuable as-is without having to wait for these cases to be sorted out. Both have to do with triality automorphisms, and would be somewhat fiddly to get right.
(If anyone has code or ready descriptions for these cases, I would be happy to include it for future releases.)

> GRP[208]:=[208,65784756654489600,"O",[9,3]]
> Error, mixed triality not yet done at
> /home/dennis/GAP4.10.1/gap-4.10.1/grp/simple.gi:859 called from
> EFactors( Gcd( 2, (par[2] - 1) ) ^ 2, expo, 6 ) at
> /home/dennis/GAP4.10.1/gap-4.10.1/grp/simple.gi:1047 called from
> DataAboutSimpleGroup( id ) at

DataAboutSimpleGroups calculates (beyond what IsomorphismTypeInfoFiniteSimpleGroup does) — among other things — the structure of the outer automorphism group.
For type D4 this involves also the triality automorphism, and the current code does not yet consider its interaction with field automorphisms — thus the error message.

> GRP[211]:=[211,67671071404425216,"U",[3,127]]
> Error, Can't do yet at
> /home/dennis/GAP4.10.1/gap-4.10.1/grp/simple.gi:577 called from
> CallFuncList( SimpleGroup, b ) at

This would be the Chevalley group of type 3D4(4). The simple groups code does not construct groups as Chevalley groups, but as classical groups of from existing libraries. I am not aware of an existing library that contains a representation of 3D4(4).
(The same holds for any larger fields and certain other large exceptional groups).

Regards,

  Alexander Hulpke


> /home/dennis/GAP4.10.1/gap-4.10.1/grp/simple.gi:696 called from
> 0 = cnt mod len at SimpleGroupList.gap:83 called from
> <function "ListSimpleShortNoL2">( <arguments> )
> called from read-eval loop at *stdin*:5
> you can 'quit;' to quit to outer loop, or
> you can 'return;' to continue
> brk> return;
> Error, Variable: 'g' must have an assigned value in
>  if s <> fail and not HasName( g ) then
>    SetName( g, s );
> fi; at /home/dennis/GAP4.10.1/gap-4.10.1/grp/simple.gi:629 called from 
> CallFuncList( SimpleGroup, b ) at
> /home/dennis/GAP4.10.1/gap-4.10.1/grp/simple.gi:696 called from
> 0 = cnt mod len at SimpleGroupList.gap:83 called from
> <function "ListSimpleShortNoL2">( <arguments> )
> called from read-eval loop at *stdin*:5
> you can 'return;' after assigning a value
> brk> 
> 
> 
> 
> 
> 
> Ok, I tried the NOSL2 option, and ran into another problem.
> 
> 
> Keith
> 
> 
> 
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